[petsc-dev] [petsc-checkbuilds] PETSc blame digest (next) 2016-04-08

Tue Apr 12 22:45:43 CDT 2016

  The session is to trust the warning, fix the potential bug, and don't blinding initiaizel variables at declaration to hide the warning.

   Thanks Satish, beyond the call of duty!

   Barry

> On Apr 12, 2016, at 10:42 PM, Satish Balay <balay at mcs.anl.gov> wrote:
> 
> Ok - I see the bug in this code.
> 
> static PetscErrorCode DMPlexReferenceTreeRestoreChildrenMatrices_Injection(DM refTree, Mat inj, PetscScalar ****childrenMats)
> 
> Since this funciton is defined as 'static' the compiler is doing
> 'inter procedure analysis' across the calling function with -O [this
> warning comes up only with -O build]
> 
> 1. plextree.c:3506 has the following variable declared [uninitialized]
>  PetscScalar    ***childrenMats;
> 
> 2. the next usage of this variable is: plextree.c:3846
>  ierr = DMPlexReferenceTreeGetChildrenMatrices_Injection(refTree,injRef,&childrenMats);CHKERRQ(ierr);
> 
> 3. Within this function - the first usage of this variable is plextree.c:L3453
>  refPointFieldMats = *childrenMats;
> 
> i.e access/use of uninitialized variable.
> 
> The following supresses the warning - but there is clearly some lurking bug..
> 
> diff --git a/src/dm/impls/plex/plextree.c b/src/dm/impls/plex/plextree.c
> index 2ee02d0..e51f704 100644
> --- a/src/dm/impls/plex/plextree.c
> +++ b/src/dm/impls/plex/plextree.c
> @@ -3503,7 +3503,7 @@ PetscErrorCode DMPlexComputeInjectorTree(DM coarse, DM fine, PetscSF coarseToFin
>   PetscLayout    rowMap, colMap;
>   PetscInt       rowStart, rowEnd, colStart, colEnd, *nnzD, *nnzO;
>   PetscObject    injRefObj;
> -  PetscScalar    ***childrenMats;
> +  PetscScalar    ***childrenMats=0;
>   PetscErrorCode ierr;
> 
>   PetscFunctionBegin;
> 
> And this was introduced by http://bitbucket.org/petsc/petsc/commits/f30e825d
> 
> Satish
> 
> On Fri, 8 Apr 2016, Barry Smith wrote:
> 
>> 
>>  Toby,
>> 
>>   We'll be filtering out these false positives. It is just taking us a couple of days to determine that needs to be filtered.
>> 
>>  Barry
>> 
>>> On Apr 8, 2016, at 2:36 PM, Tobin Isaac <tisaac at uchicago.edu> wrote:
>>> 
>>> 
>>> I spent a couple minutes verifying that there is no code path where
>>> that variable is not initialized on line 3437.
>>> 
>>> -Wmaybe-uninitialized seems to generate a lot of false positives.
>>> Coupled with the blame digest's poor ability to assign blame, this
>>> proactive approach seems to waste more time than a reactive
>>> SEGV->valgrind->fix approach.
>>> 
>>> Cheers,
>>> Toby
>>> 
>>> On Fri, Apr 08, 2016 at 02:12:22PM -0500, Satish Balay wrote:
>>>> This should have been sent to Toby.
>>>> 
>>>> I don't really understand the issue here. Its triggered by --with-debugging=0. I'm
>>>> not sure why these compilers are pointing to petscsys.h. I get slightly different message
>>>> on my laptop.
>>>> 
>>>> mpicc -c -fPIC  -Wall -Wwrite-strings -Wno-strict-aliasing -Wno-unknown-pragmas -fvisibility=hidden -g -O   -I/home/balay/petsc/include -I/home/balay/petsc/arch-linux2-c-opt/include -I/home/balay/soft/mpich-3.1.4/include    -MMD -MP /home/balay/petsc/src/dm/impls/plex/plextree.c -o arch-linux2-c-opt/obj/src/dm/impls/plex/plextree.o
>>>> /home/balay/petsc/src/dm/impls/plex/plextree.c: In function ‘DMPlexComputeInjectorTree’:
>>>> /home/balay/petsc/src/dm/impls/plex/plextree.c:3484:11: warning: ‘childrenMats’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>>>>  ierr = PetscFree(refPointFieldMats);CHKERRQ(ierr);
>>>>          ^
>>>> /home/balay/petsc/src/dm/impls/plex/plextree.c:3507:18: note: ‘childrenMats’ was declared here
>>>>  PetscScalar    ***childrenMats;
>>>>                 ^
>>>> 
>>>> Satish
>>>> 
>>>> On Fri, 8 Apr 2016, PETSc checkBuilds wrote:
>>>> 
>>>>> 
>>>>> 
>>>>> Dear PETSc developer,
>>>>> 
>>>>> This email contains listings of contributions attributed to you by
>>>>> `git blame` that caused compiler errors or warnings in PETSc automated
>>>>> testing.  Follow the links to see the full log files. Please attempt to fix
>>>>> the issues promptly or let us know at petsc-dev at mcs.anl.gov if you are unable
>>>>> to resolve the issues.
>>>>> 
>>>>> Thanks,
>>>>> The PETSc development team
>>>>> 
>>>>> ----
>>>>> 
>>>>> warnings attributed to commit https://bitbucket.org/petsc/petsc/commits/49d7da5
>>>>> PetscMalloc: allow ptr=malloc(0) and free(ptr)
>>>>> 
>>>>> include/petscsys.h:1157
>>>>>   [http://ftp.mcs.anl.gov/pub/petsc/nightlylogs/archive/2016/04/08/build_next_arch-freebsd-cxx-pkgs-opt_wii.log]
>>>>>     /usr/home/balay/petsc.clone-2/include/petscsys.h:1157:88: warning: 'childrenMats' may be used uninitialized in this function [-Wmaybe-uninitialized]
>>>>>   [http://ftp.mcs.anl.gov/pub/petsc/nightlylogs/archive/2016/04/08/build_next_arch-linux-opt-cxx-quad_grind.log]
>>>>>     /sandbox/petsc/petsc.clone-3/include/petscsys.h:1157:88: warning: 'childrenMats' may be used uninitialized in this function [-Wmaybe-uninitialized]
>>>>>   [http://ftp.mcs.anl.gov/pub/petsc/nightlylogs/archive/2016/04/08/build_next_arch-freebsd-pkgs-opt_wii.log]
>>>>>     /usr/home/balay/petsc.clone/include/petscsys.h:1157:39: warning: 'childrenMats' may be used uninitialized in this function [-Wmaybe-uninitialized]
>>>>>   [http://ftp.mcs.anl.gov/pub/petsc/nightlylogs/archive/2016/04/08/build_next_arch-linux-pkgs-latest_cg.log]
>>>>>     /sandbox/petsc/petsc.clone-4/include/petscsys.h:1157:25: warning: 'childrenMats' may be used uninitialized in this function [-Wmaybe-uninitialized]
>>>>>   [http://ftp.mcs.anl.gov/pub/petsc/nightlylogs/archive/2016/04/08/build_next_arch-linux-pkgs-opt_crank.log]
>>>>>     /sandbox/petsc/petsc.clone/include/petscsys.h:1157:25: warning: 'childrenMats' may be used uninitialized in this function [-Wmaybe-uninitialized]
>>>>> 
>>>>> ----
>>>>> To opt-out from receiving these messages - send a request to petsc-dev at mcs.anl.gov.
>>>>> 
>>> 
>> 
>> 